Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B81—MICROSTRUCTURAL TECHNOLOGY
  • B81C—PROCESSES OR APPARATUS SPECIALLY ADAPTED FOR THE MANUFACTURE OR TREATMENT OF MICROSTRUCTURAL DEVICES OR SYSTEMS
  • B81C1/00—Manufacture or treatment of devices or systems in or on a substrate
  • B81C1/00015—Manufacture or treatment of devices or systems in or on a substrate for manufacturing microsystems
  • B81C1/00261—Processes for packaging MEMS devices
  • B81C1/00277—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS
  • B81C1/00285—Processes for packaging MEMS devices for maintaining a controlled atmosphere inside of the cavity containing the MEMS using materials for controlling the level of pressure, contaminants or moisture inside of the package, e.g. getters
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/0045—Photosensitive materials with organic non-macromolecular light-sensitive compounds not otherwise provided for, e.g. dissolution inhibitors
• • G—PHYSICS
  • G03—PHOTOGRAPHY; CINEMATOGRAPHY; ANALOGOUS TECHNIQUES USING WAVES OTHER THAN OPTICAL WAVES; ELECTROGRAPHY; HOLOGRAPHY
  • G03F—PHOTOMECHANICAL PRODUCTION OF TEXTURED OR PATTERNED SURFACES, e.g. FOR PRINTING, FOR PROCESSING OF SEMICONDUCTOR DEVICES; MATERIALS THEREFOR; ORIGINALS THEREFOR; APPARATUS SPECIALLY ADAPTED THEREFOR
  • G03F7/00—Photomechanical, e.g. photolithographic, production of textured or patterned surfaces, e.g. printing surfaces; Materials therefor, e.g. comprising photoresists; Apparatus specially adapted therefor
  • G03F7/004—Photosensitive materials
  • G03F7/0047—Photosensitive materials characterised by additives for obtaining a metallic or ceramic pattern, e.g. by firing
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P76/00—Manufacture or treatment of masks on semiconductor bodies, e.g. by lithography or photolithography
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10P—GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10
  • H10P76/00—Manufacture or treatment of masks on semiconductor bodies, e.g. by lithography or photolithography
  • H10P76/20—Manufacture or treatment of masks on semiconductor bodies, e.g. by lithography or photolithography of masks comprising organic materials
  • H10P76/202—Manufacture or treatment of masks on semiconductor bodies, e.g. by lithography or photolithography of masks comprising organic materials for lift-off processes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T428/00—Stock material or miscellaneous articles
  • Y10T428/24—Structurally defined web or sheet [e.g., overall dimension, etc.]
  • Y10T428/24479—Structurally defined web or sheet [e.g., overall dimension, etc.] including variation in thickness
  • Y10T428/24612—Composite web or sheet
  • Y10T428/2462—Composite web or sheet with partial filling of valleys on outer surface

Definitions

• the present invention relates to a process for the formation of miniaturized deposits of getter materials, namely, deposits having lateral dimensions lower than one millimeter, and generally from a few micrometers to hundreds of micrometers.
• the invention also relates to deposits of getter materials so obtained.
• the getter materials have the characteristic of being able to fix gaseous traces such as hydrogen, oxygen, carbon oxides, water vapor and, in some cases, nitrogen. These materials are generally metals belonging to the III, IV and V transition group (groups of the scandium, titanium and vanadium) or alloys thereof with other elements, generally transition metals or aluminum.
• the most widely employed getter materials are titanium-based alloys and, in particular, zirconium-based alloys.
• MEMS MicroElectroMechanical Systems
• MOEMS MicroOptoElectroMechanical Systems
• These devices comprise a sealed cavity inside which a micromechanical part able to perform a predefined movement or parts able to interact with an electromagnetic radiation are present, in addition to auxiliary parts and electrical feedthroughs both for supplying the device and for the transmission of signals to the outside.
• microaccelerometers described in numerous patents as US 5,594,170, US 5,656,77S and US 5,952,572
• miniaturized resonators used in the telecommunications field and particularly in the manufacturing of mobile phones, described in patents US 5,821,836 and US 6,058,027
• miniaturized IR sensors an example of which is described in patent US 5,895,233.
• getter material capable of removing these gases.
• getter materials in MEMS devices is described, e.g. in patents US 5,952,572, 6,499,354, 6,590,850, 6,621,134, 6,635,509 and in patent application US-A1-2003/0138656.
• the cavity has extremely reduced dimensions, and the getter can be inserted only in the form of a thin layer, being of lateral dimensions between hundreds of micrometers ( ⁇ m) and a few millimeters, and with thicknesses varying between fractions of ⁇ m and a few ⁇ m.
• the MEMS are manufactured with technologies derived from those of semiconductors, where thousands of miniaturized devices are simultaneously manufactured on a single support (commonly a silicon wafer), by means of localized deposits and selective removals of layers of different materials. For these productions, it is necessary to be able to grant both dimensional and positioning precision of the various layers deposited, and this also applies to the deposits of getter materials.
• a technique allowing to produce thin deposits with a high precision of dimensions and of the deposits positioning is the one known as "lift-off', which consists in forming a layer of photohardening polymeric material on a support (these materials are known in the field as “resist”); selectively exposing the polymeric layer by means of a mask, generally to UV radiations; selectively removing with a first solvent the previously unexposed part (or the exposed one, according to the resist and the solvent type); depositing on the support and on the resist not removed by the first solvent a thin layer of the desired material, e.g.
• the support on which forming the thin layer is desired and a "target" of the material desired to be deposited are arranged in a process chamber; the chamber is first evacuated and subsequently filled with a noble gas atmosphere, commonly argon or krypton, at a pressure generally comprised between about 0.01 and 0.1 Pascal (Pa); by applying a potential difference of some thousands of Volt between the support holder and the target holders (so that the latter is at the cathodic potential), a plasma of ions Ar + (or Kr + ) is created, which are accelerated by the electric field towards the target causing impact erosion thereof; the species (generally atoms or clusters of atoms) resulting from the erosion of the target deposit on the support thus forming the thin layer.
• a noble gas atmosphere commonly argon or krypton
• a first problem occurring is that, during sputtering, an overheating of the resist and the consequent hardening thereof take place, whereby the resist layer can no more be removed with solvents; the problem is well known in the field, and it is described, e.g., in article "Low-noise MOSFET with sputtered amorphous metal gate defined by lift-off, by N. A. Papanicolaou et al., Inst. Phys. Conf. Ser. No. 65, pags 407-414 (see pag. 411 in particular).
• this article suggests to cool the support during the deposition at a temperature of about 10 °C; however, in addition to rendering the apparatus complex, this has the consequence of reducing the density of the deposited layer, which is an effect not generally desired in productions wherein the lift-off is adopted.
• the second problem of the use of sputtering is that in this technique the material deposition is not directional, i.e. the material deposits on the support in all directions rather than in a preferential direction (as it happens, on the contrary, with evaporation).
• This characteristic causes the target material to deposit uniformly on all the available surfaces, forming a continuous layer on the upper surface of the resist, at the bottom of the cavities formed in the resist (i.e. on the support exposed zones) and on the lateral walls, made of resist, of these cavities.
• the continuity of the deposited layer prevents the subsequent access of the second solvent to the resist and hence the removal thereof from the support surface.
• a first expedient is to provide that a recess (known in the field as “undercut” or “notch”) is present under the resist layer along the whole periphery of the cavity, sufficiently deep to be only barely filled with the material being deposited; in this way the continuity of the deposited layer is interrupted, thus leaving a way of access to the solvent in order to reach the contact zone between the resist and the support surface.
• undercut or "notch”
• the formation of the recess generally requires that the resist layer is actually a double layer of different polymeric materials, with different solubility characteristics in different solvents, so that the lower layer (the one in direct contact with the support) is attacked by the first solvent more rapidly than the upper one; this approach is illustrated, for example, in patent US 5,705,432 and in patent applications EP 341,843 and WO 03/043062.
• a collimator that is a mechanical filter intercepting the particles moving in directions non-perpendicular (or nearly so) to the support, but these measures reduce the amount of material deposited on the support with respect to the one removed from the target, leading to wastes of material, to the need for replacing the target more frequently, and shortly in the raise of the process costs.
• the sputtering deposition technique has not practical industrial application as the deposition operation in lift-off processes.
• Object of the present invention is to provide a lift-off process for the formation of miniaturized getter deposits, wherein the deposition operation of the getter material is carried out by sputtering, being free from the drawbacks of the prior art.
• the cathodic deposition operation is not preceded by either operations or treatments for the formation of recesses in the lower part of the polymeric layer, and in that said cathodic deposition operation is carried out with a chamber pressure comprised between about 1 and 5 Pa and with a specific power comprised between 6 and 13 W per square centimeter of area of the target actually interested by the plasma.
• the specific power on the target in the process of the invention has different characteristic values from those typically used in sputtering processes, which are generally comprised between about 20 and 40 W/cm 2 .
• specific power as used in the text and in the claims, it is intended the power applied divided by the area of the target portion which is in contact with the plasma of ions of the noble gas employed: it is well known in the field that the target zone actually interested by the plasma is only a fraction of the surface of the same, which can have the geometry of a circular crown in the simplest case, but that can have more complex geometries.
• the geometry of the zone actually interested by the plasma can be controlled, e.g., by magnetic fields ("magnetron" mode sputtering, well known by those skilled in the art), and it is also known that it is possible to move the zone involved during the process, in order to have, on average, a more uniform erosion of the target.
• magnetic fields magnetic fields
• Figure 1 shows, in cross-section, a support at various steps of the lift-off process: the dimensions in the drawing are not full-scale, and particularly heights and thicknesses are greatly increased for a clarity purpose.
• the first step of the lift-off process of the invention consists in the choice of the support, 10 (Figure l.a).
• the support can be metallic, ceramic, glass, quartz or it can be made of a semiconductor material, possibly with a passivation layer (made, e.g., of silicon oxide or silicon nitride) on the surface onto which the subsequent operations will be carried out; the material choice depends on the final use of the getter device produced in the process.
• the material of most common use is mono- or polycrystalline silicon, which is commercially available in wafer of a variable diameter between about 10 and 30 cm with thicknesses from some tenths of millimeter to about 1 mm.
• the second step of the process consists in forming a layer of a photohardening polymeric material, 11 ( Figure l.b) on support 10; photohardening materials are known in the field under the name "photoresist".
• the layer 11 can produced "in situ” by uniformly distributing a liquid material on the support and by making it consolidate onto the support; typically this operation is carried out by "spin-coating", consisting in depositing a suitable amount of solution containing an organic material at the center of the support, set the support in fast rotation so that the solution is spread, and making the solvent evaporate, leaving an even layer of the organic material on the support; the solvent evaporation is generally promoted by heating after formation of the said layer is completed.
• dry-film that is a polymeric film corresponding to the desired polymeric layer as to thickness and composition, which is uniformly adhered to the support by laying it off with a heated roll;
• a dry film suitable for the objects of the invention is the product ORDYL FP 325 sold by the company TOK Italia S.p.A. of Pogliano Milanese (Milan).
• the layer 11 so laid is selectively made sensitive by lighting, through photolithographic methods well known in the field; in Figure 1.c the arrows indicate the light radiation (generally UV) and the dark parts of layer 11 are the zones photosensitivized, i.e. having undergone such chemical variations that they have a solubility in a predefined solvent different from the one of the zones not exposed.
• the light radiation generally UV
• the dark parts of layer 11 are the zones photosensitivized, i.e. having undergone such chemical variations that they have a solubility in a predefined solvent different from the one of the zones not exposed.
• a so-called "development solution” for example, if film 11 has been produced by spin- or spray-coating of a solution of the MICROPOSIT ® S-1800 series, suitable development solutions are those of the MICROPOSIT ® MF-300 series by Shipley Company, while in the case of use of ORDYL dry- film, a suitable solvent is a 1% by weight sodium carbonate aqueous solution; the result of this operation is shown in Figure l.d, and consists of support 10 with a deposit 11 having apertures 12, 12', ....
• the subsequent operation is the deposition of the getter material by sputtering, schematically represented in Figure 1.e, wherein the dots represent the particles of the material under deposition and the wavy arrows represent the depositing direction of these particles.
• This operation is the one characterizing the process of the invention: first of all, the sputtering deposition is not preceded by treatments of layer 11 directed to form recesses in the zones contacting the support like in the processes of the prior art.
• the deposition is carried out under conditions that are not typical for this technique, in particular with a working pressure in chamber being of one or two orders of magnitude greater with respect to the values normally employed in the field and with a relatively low applied power: the pressure in the chamber during sputtering, when using argon, is comprised between about 1 and 5 Pa and preferably between about 1.5 and 4 Pa, and the power applied, working e.g. with a target of about 16.5 cm diameter, can vary between about 500 and 1000 W.
• the support temperature and the distance between target and support are other deposition parameters. With respect to temperature, the support can be cooled during deposition.
• the target-support distance is greater than 40 mm and it is preferably between about 50 and 80 mm; also this parameter is not typical of cathodic depositions, which are generally carried out with smaller target-support distances, e.g. of about 10 mm. Controlling these two parameters is however not necessary for the purposes of the invention, contrary to chamber pressure and specific power.
• target and support In order to increase the porosity of the deposited getter material layer, it is also possible to arrange target and support so that the facing surfaces thereof are not parallel, and to move (rotate, for example) the support during the deposition.
• a thin layer, 13, of getter material is obtained, covering both the zones of support 10 corresponding to apertures 12, 12', ..., and the portions of polymeric layer 1 1 not previously removed.
• the last step of the process of the invention consists in the removal with a solvent of the portions of polymeric deposit 11 still present on support 10.
• this operation is the one which is practically impossible to carry out in the prior art processes, unless the particular expedients cited are used, especially the formation of an "undercut" under layer 11 at the periphery of apertures 12, 12', ...; on the contrary, the inventors have observed that by carrying out the sputtering operation in the particular above-described conditions, the removal of layer 11 with the solvent occurs in an effective manner, without using said particular expedients.
• a solvent for the removal of layer 11 it is possible to use products of the MICROPOSIT ® REMOVER series if the layer has been produced from MICROPOSIT solutions, or a sodium hydroxide solution at 40-50 0 C in the case of ORDYL dry-film.
• the final result of the operation, and of the whole process, is the support 10 with localized deposits 131, 131', ..., shown in Fig. l.g. Deposits 131, 131', ... can have a minimum thickness of about 0.5 ⁇ m; in fact, it has been observed that with lower thickness the gas sorption properties are excessively reduced, maybe due to the fact that too thin deposits tend to reproduce the morphology of the surface on which they grow, and thereby result too smooth and compact to have good sorption characteristics.
• the maximum thickness is, on the contrary, determined by compromise considerations between having a sorption ability compatible with the desired application, and the time (and thereby the cost) of the formation of the deposit; in addition, deposits being excessively thick tend to detach from the support. Suitable deposits for the invention have maximum thicknesses of about 20 ⁇ m, and preferably comprised between about 1 and 5 ⁇ m.
• the process of the invention comprises a further step between the step of forming in the polymeric layer at least a cavity with a first solvent, and the step of depositing the getter material by sputtering.
• This further optional step is a thermal treatment of the portion of the polymeric layer left on the support by the previous treatment of removal with the first solvent.
• This operation has the result of hardening the polymer, so that during the subsequent deposition of the getter by sputtering, the polymer has better mechanical characteristics and thus improved capability to maintain the pattern obtained during the selective removal with the first solvent.
• this operation is known in the field of processes of deposition of thin films, and referred to for instance as "post-development baking". The temperature required to carry out this operation depends on the chemical nature of the polymer; with the materials described previously, this operation may range between about 100 and 150 °C.
• Figure 2 is the reproduction of a photograph, obtained with the optical microscope, of a portion of a support of the type 10 on which getter material deposits of complex geometry have been obtained with the process of the invention; in the drawing, the various getter deposits are altogether indicated as element 20, while zones of the surface of the support (silicon made, in this case) resulting exposed at the end of the liftoff process are indicated as 21.
• the deposits have clear and straight edges, confirming the high precision of dimensioning and positioning of the individual deposits, which is possible to obtain with the process of the invention, hi particular, the deposits shown in the drawing have a thickness of about 2 ⁇ m, the zones of deposits 20 having elongated linear shape have a width of about 120 ⁇ m, while the exposed zones 21 have a width of about 100 ⁇ m; these dimensions, particularly the lateral ones, as well as the positioning precision shown in the drawing, could not be obtained in a precise and reproducible way with other methods of getter material layers deposition.

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• Engineering & Computer Science (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Manufacturing & Machinery (AREA)
• Physics & Mathematics (AREA)
• General Physics & Mathematics (AREA)
• Chemical & Material Sciences (AREA)
• Ceramic Engineering (AREA)
• Spectroscopy & Molecular Physics (AREA)
• Physical Vapour Deposition (AREA)
• Manufacture Of Electron Tubes, Discharge Lamp Vessels, Lead-In Wires, And The Like (AREA)
• Common Detailed Techniques For Electron Tubes Or Discharge Tubes (AREA)
• Drying Of Semiconductors (AREA)
• Electrodes Of Semiconductors (AREA)
• Electrostatic, Electromagnetic, Magneto- Strictive, And Variable-Resistance Transducers (AREA)
• Yarns And Mechanical Finishing Of Yarns Or Ropes (AREA)
• Image-Pickup Tubes, Image-Amplification Tubes, And Storage Tubes (AREA)
• Exposure Of Semiconductors, Excluding Electron Or Ion Beam Exposure (AREA)
• Portable Nailing Machines And Staplers (AREA)
• Cathode-Ray Tubes And Fluorescent Screens For Display (AREA)
• Exposure And Positioning Against Photoresist Photosensitive Materials (AREA)

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Applications Claiming Priority (2)

Publications (2)

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• 2005
  • 2005-04-12 IT IT000616A patent/ITMI20050616A1/it unknown
• 2006
  • 2006-04-11 CA CA2602808A patent/CA2602808C/en not_active Expired - Lifetime
  • 2006-04-11 EP EP06745274A patent/EP1869696B1/de not_active Expired - Lifetime
  • 2006-04-11 CN CN2006800116590A patent/CN101156227B/zh not_active Expired - Lifetime
  • 2006-04-11 AT AT06745274T patent/ATE398831T1/de active
  • 2006-04-11 DE DE602006001518T patent/DE602006001518D1/de not_active Expired - Lifetime
  • 2006-04-11 KR KR1020077022069A patent/KR100930738B1/ko not_active Expired - Lifetime
  • 2006-04-11 DK DK06745274T patent/DK1869696T3/da active
  • 2006-04-11 PL PL06745274T patent/PL1869696T3/pl unknown
  • 2006-04-11 WO PCT/IT2006/000242 patent/WO2006109343A2/en not_active Ceased
  • 2006-04-11 US US11/911,065 patent/US7998319B2/en active Active
  • 2006-04-11 JP JP2008506057A patent/JP4971305B2/ja not_active Expired - Lifetime
  • 2006-04-11 ES ES06745274T patent/ES2308746T3/es not_active Expired - Lifetime
• 2007
  • 2007-09-03 NO NO20074482A patent/NO338707B1/no unknown

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